Helium film refrigerator



June 3, 1969 D. Goons-rem 3,447,333

HELIUM FILM REFRIGERATOR Filed March 17, 1967 FIG. 1.

FIG. 2.

//V VE/V 70/2 0/4 V/D L. 60005 TE/A/ B) HA5 A7702/V4E'X5" b Aee/a; 16750;; #055541. (2 KERN United States Patent Int. Cl. F251) 19/00 US. Cl. 6245 16 Claims ABSTRACT OF THE DISCLOSURE A refrigerator utilizing helium 4 for operation below 1 K. A refrigerator incorporating a reservoir of liquid helium 4 in the superfluid state, with a passage for flow of the helium 4 to an evaporation chamber to form a film for evaporation and cooling.

This invention relates to refrigeration and, in particular, to refrigerators for producing temperatures below 1 K. and down to 0.5 K. and lower.

Various materials have been utilized in obtaining very low temperatures, including the helium isotopes, helium 3 and helium 4. Apparatus incorporating helium 3 has successfully achieved temperatures below 1 K. However, helium 3 is very rare and expensive, and complicated equipment and procedures are involved in recovering the helium 3. Helium 4 is more readily available and is usually vented to the atmosphere during operation of refrigeration apparatus utilizing helium 4. However, conventional apparatus and methods using helium 4 have not been able to reach 1 K. with any refrigeration capacity.

It is an object of the present invention to provide new and improved apparatus and methods using helium 4 for obtaining temperatures below 1 K. A further object is to provide a refrigerator wherein a film of helium 4 is evaporated to provide cooling, with the film being continuously replenished from a helium 4 source.

It is an object of the invention to provide a new and improved refrigerator including a film evaporation chamber, a reservoir of helium 4 maintained in the superfluid state, and means for flowing helium 4 from the reservoir to the evaporation chamber at a controlled rate. A further object of the invention is to provide such a refrigerator which may utilize conventional vacuum pumping equipment and conventional vacuum techniques in achieving the desired low temperatures.

The invention also comprises novel details of construction and novel combinations and arrangements of parts, which will more fully appear in the course of the following description. The drawing merely shows and the description merely describes preferred embodiments of the present invention which are given by way of illustration or example.

In the drawing:

FIG. 1 is a vertical sectional view of a preferred embodiment of the refrigerator;

FIG. 2 is a similar view of an alternative embodiment of the refrigerator; and

FIG. 3 is a partial vertical sectional view of an alternative form of the evaporating structure of FIG. 1.

3,447,333 Patented June 3, 1969 The refrigerator of the invention contemplates maintenance of a reservoir of helium 4 in the superfluid state, flow of the superfluid helium 4 from the reservoir to an evaporation chamber through a very small opening to provide a film of the helium 4 in the evaporation chamber, and evaporation of the film. The small opening limits the flow of film to a rate which can be handled by the evaporation system and the opening typically may be a superleak. With this arrangement, there is no accumulation of fluid in the evaporation chamber and no liquid contact with the warmer portions of the refrigerator. It appears that temperatures in the order of 05 K. can be obtained with a refrigeration capacity in the order of 240 ergs per second.

The apparatus of FIG. 1 includes a cup-shaped container 10 having a chamber 11 in the upper portion thereof, with the container 10 supported from a tube or sleeve 12 which in turn is supported from another tube or sleeve 13. A container 14 is also carried on the tube 13 disposed around and spaced from the container 10. The tube 13 with its attachments may be positioned within another container 15.

The lower portion 17 of the container 10 may comprise the experimental space. A quantity of helium 4 is placed in the chamber 11 and a flow passage to the chamber 18 within the tube 12 is provided by a small opening 19. A vacuum pump 20 is connected to the space between the containers 14, 15. Another vacuum pump 21 with a condensation system is connected to the interior of the tube 13. Another vacuum pump 22 is connected to the space between the containers 10, 14 via a line 23. The condensation system and pumps may be conventional equipment of the type presently available.

The refrigeration occurs in the chamber 18, with liquid helium 4 flowing from the chamber 11 through the opening 19 into the chamber 18. The helium in the chamber 11 is maintained in the superfluid state, that is, at a temperature below 22 K., typically about 1.2 K. When in the superfluid state, the liquid helium Will form a thin film which flows up the wall of the chamber 11, through the opening 19, and along the wall of the chamber 18. An evaporating structure may be incorporated in the chamber 18 to provide a high surface-to-volume ratio for increasing the surface over which the film of liquid helium can form. A typical evaporating structure is a copper sponge 25. An alternative structure may be a plurality of fins 25a of conventional shape as shown in FIG. 3.

The liquid helium film is evaporated in the chamber 18 by the action of the pump 21 and is withdrawn from the chamber through the tube 13. The helium vapor may be condensed and recovered or may be vented to the atmosphere.

The container 14 provides a vacuum isolation jacket around the refrigerator. The container 15 typically is filled with liquid helium for further isolation and for initial cooling of the refrigerator. Another nitrogen isolation jacket may be provided about the liquid helium jacket if desired.

The rate of flow of the helium 4 from the chamber 11 to the chamber 18, and the rate of pumping by the pump 21 are selected so that the film of helium in the chamber 18 will be evaporated without permitting formation of a pool or puddle of liquid helium in the chamber 18. The

container and the tube 12 preferably are made of copper or similar material having high thermal conductivity, for obtaining maximum heat transfer between the chamber 18, the chamber 11, and the space 17. The containers 14 and 15 preferably are made of glass or similar material having low thermal conductivity for maximum isolation. The tube 13 may be made of stainless steel or similar material having relatively low thermal conductivity for maximum thermal isolation. A copper sponge 26 or fins or similar structure may be provided on the bottom of the chamber 11 for improved thermal contact between the chamber 11 and the space 17.

In -a typical structure, a few cubic centimeters of liquid helium 4 may be positioned in the chamber 11. The opening 19 may be in the order of 0.5 mm. diameter, with film flow therethrough at the rate of about 10- grams per second. The pump 21 is capable of handling 10'- grams per second at about 10 mm. mercury pressure, which corresponds to a temperature of about 05 K. The container 15 may be about five inches diameter and three feet tall, and the container 14 about two-inches diameter and six inches tall. Apparatus of this type utilizing the evaporation of a film of helium 4 has been operated to achieve temperatures below 1 K.

An alternative form of the invention is illustrated in FIG. 2. A container has a smaller diameter lower portion with a quantity of activated charcoal 31 positioned therearound. The container 30 terminates in a flow passage in the form of a superleak 32 which opens onto a tray 33. A copper sponge 34 may be carried on the tray or may take the place of the tray. The sponge and/or tray may be supported from the tube 32. An experiment container 35 may be carried on the tray 33 by a block 36.

A radiation shield 38 in the form of a sheet of copper may be afiixed to the container 30 adjacent the upper end of the shield. The lower portion 38a of the shield may be removable to provide access to the container 35. The container 30 is positioned in another container 37 and perforations are provided in the shield 38 for flow from the interior to the exterior of the shield. The interior of the container 37 is connected through a valve 39 to a vacuum pump 40. The interior of the container 30 is connected to another vacuum pump 41.

The superleak 32 provides for flow of the superfluid helium 4 at a controlled rate from the container 30 to the tray 33. Typically the superleak may comprise a stainless steel or copper-nickel capillary packed with jewelers rouge. Another form of superleak comprises a length of wire positioned within a glass tube, with the glass tube heated and drawn to form the tube about the wire.

In operation, a vacuum is drawn in the container 37 by the pump 40, after which the valve 39 is closed. Liquid helium 4 is introduced into the container 30 and is pumped down to about 1.2 K. by the pump 41. The helium 4 is now in the superfluid state and a film flows down through the tube 32 onto the tray 33. The activated charcoal 31 acts as an adsorption pump for evacuating the helium from the evaporation chamber. That is to say, the liquid helium flows from the container 30 through the tube 32 to form a film at the tray 33. The helium is evaporated into the chamber and the helium vapor is then adsorbed onto the charcoal. The energy extracted from the chamber goes into the liquid helium pool in the container 30 and is removed by the pump 41. With this arrangement, a single conventional pump working at relatively high pressures, in the order of 1 mm. of mercury, will handle the pumping requirements for refrigeration below 1 K. and down to about 05 K.

At the end of a run, the helium on the charcoal is removed by the pump 40. As with the embodiment of FIG. 1, the rate of flow of film onto the tray 33 and the quantity of charcoal are selected so that the helium film will be evaporated from the tray without formation of a pool or puddle of liquid.

4' Although" exemplary embodiments of the invention have been disclosed and discussed, it will be understood that other applications of the invention are possible and that the embodiments disclosed may be subjected to various changes, modifications and substitutions without necessarily departing from the spirit of the invention.

I claim as my invention:

1. A method of developing a very low temperature for a refrigerator or the like including the steps of:

cooling a quantity of helium 4 to the superfluid state;

flowing the superfluid helium 4 to an evaporation chamber at a controlled rate to produce a fluid film in the chamber; and

evaporating the film of the helium 4 and removing the vapor from the chamber without accumulating liquid helium 4 in the chamber. 2. A method asdefined in claim 1 including the step of vacuum pumping the evaporated helium 4 from the chamber. 3. A method as defined in claim 1 including the steps of adsorbing the evaporated 'helium 4 onto an adsorbent material, and subsequently removing the adsorbed helium 4 from the adsorbent material by vacuum pumping.

4. In a refrigerator, the combination of: a first chamber; 1 a quantity of helium .4 in said first chamber; means forcooling said helium 4 to the superfluid state; a second chamber; 3 means defining a flow passage connecting said first chamber to said second chamber for controlling flow of said helium 4 to said second chamber, with said helium 4 forming a film in said second chamber; and

means for evaporating said film of helium 4 from said second chamber without accumulating liquid helium 4 in said second chamber.

1 5. An apparatus as defined in claim 4 in which said flow passage comprises a superleak.

6. An apparatus as defined in claim 4 including an evaporating structure in said second chamber having a high surface-to-volume ratio.

7. An apparatus as defined in claim 6 in which said evaporating structure comprises a plurality of fins.

8. An apparatus as defined in claim 6 in which said evaporating structure comprises a metal sponge.

9'. An apparatus as defined in claim 4 in which said means for evaporating includes a vacuum pump and a line interconnecting said pump and said second chamber.

10. An apparatus as defined in claim 4 in which said means for evaporating includes a quantity of activated charcoal.

11. An apparatus as defined in claim 4, including:

a first container with said first and second chambers disposed therein; and

means defining an experiment container mounted in said first container adjacent said first and second chambers.

12. An apparatus as defined in claim 4 including means for producting a vacuum in said chamber, and wherein said means for evaporating comprises a quantity of activated charcoal disposed in said second chamber for evaporating said helium 4.

13. An apparatus as defined in claim 12 in which said first chamber is disposed within said second chamber, with said activated. charcoal mounted on said first chamber.

14. An apparatus as defined in claim 13 including means defining an evaporation surface supported within said second chamber, with said flow passage conducting said helium 4 onto said evaporation surface. 7

15. An apparatus as defined in claim 14 in which said evaporation surface is supported by said means defining said flow passage. v

16. In a refrigerator, the combination of:

a first chamber;

a quantity of helium 4 in said first chamber;

a second chamber;

means defining a flow passage connecting said first chamber to said second chamber for controlling flow of said helium 4 to said second chamber, with said helium 4 forming a film in said second chamber;

a first container with said first and second chambers disposed therein;

means for producing a vacuum in said first container;

21 second container with said first container disposed therein;

a pool of liquid helium in said second container around said first container;

means for producing a vacuum in said second container; and

means for evaporating said helium 4 from said second chamber.

References Cited UNITED STATES PATENTS 3,166,915 1/1965 Klipping 62-514 XR 3,176,473 4/1965 Andonizn 62-514 XR 3,192,730 7/1965 Webb 6211 XR 3,302,419 2/1967 Walter 62-514 XR 3,314,773 4/1967 Deiness 62-514 XR 3,358,463 12/1967 Hawkins 62 514 XR MEYER PERLIN, Primary Examiner.

US. 01. X.R.s 

